Avian infectious bronchitis is an acute contagious respiratory infectious disease cause by infectious bronchitis virus. The clinical signs of infections are breathing difficulties, coughing and mouth breathing etc. Infectious bronchitis virus is a coronavirus. Its particles are spherical, with a diameter around 80˜120 nm, sometimes are polymorphic, with capsule and many pear-shape spikes. The spikes are radially arranged with about 20 nm long and nucleocapsid helical symmetry structure. Avian infectious bronchitis virus genome is a single thread-like chain of positive-strand and single-stranded RNA molecule, with the size of 27000˜32000 nt. It is the largest known RNA virus genome.
Avian infectious bronchitis is a vaccine-preventable disease. Vaccines are usually made of the virus which uses avian embryo for immune incubation reproduction. Avian infectious bronchitis virus antigen which was obtained from avian embryo usually contains a large number of avian embryo protein and other impurities. The traditional purification methods include ultra high speed centrifugation, density gradient centrifugation, sucrose gradient centrifugation. CsCl gradient centrifugation, PEG precipitation and ammonium sulfate precipitation. For example, Liu et al. teach a high-speed centrifugal separation method to purify virus in Chinese Patent application CN102628032A. These purification methods have many problems, such as, 1. Small process capacity; 2. Complex operation; 3. Introduction of exogenous impurities, such as sucrose, PEG, ammonium sulfate etc; 4. Degeneration of the virus, such as ammonium sulphate precipitation.